Silk sutures and ligatures



Feb. 14, 1956 J. NICHOLS ET AL 2,734,506

SILK SUTURES AND LIGATURES Filed DSG. 14, 1953 United States Patent SILK SUTURES AND LIGATURES Joseph Nichols, Princeton, and Thomas L Reissmann and Warren E. Collins, Bound Brook, N. l., assignors to Ethicon, Inc., a corporation of New Jersey Application December 14, 1953, Serial No. 397,928

13 Claims. (Cl. 12S-335.5)

The present invention relates to a resin impregnated silk suture for surgical purposes and to a method of impregnatng silk threads or strands.

Silk threads, made by twisting or braiding degummed and cleaned raw silk filaments have been used as suturing and ligating material for many years. Heretofore, wax has been used to impregnate silk threads to impart stiffness to improve its knot-holding properties and to render the thread nonecapillary in order to prevent the transmission of infection along its length when it is imbedded in body tissue. Wax has been applied either by hand, hot melt dipping, or by a hot stretching process. Pretreat ment of silk threads with aluminum acetate has also been practiced since this fixes the wax to the thread and retards the loss of wax during sterilization. Several disadvantages are inherent in the use of untreated silk thread for suturing or ligating. Silk thread has a tendency to broom when cut and this makes the threading of silk thread through the eye of a needle difhcult and tedious. Untreated silk threads are very flexible and the great exibility makes rapid and eicient tying of knots'difiicult. The brooming and the undesirable flexibility of untreated silk thread have been partially overcome and diminished by pretreating with aluminum acetate and coating with a wax such as beeswax, and although silk threads treated in this way have achieved acceptance by surgeons for suturing and ligating, they still have a number of inherent disadvantages. When a Wax-coated silk suture is knotted some of the wax invariably exudes from the thread as the knot is tied. Particles of exuded Wax are often deposited in tissues in the form of small particles and these are treated as foreign bodies by tissues and characteristic foreign body tissue reactions result. Wax incorporated into a braided silk strand acts to lubricate the fibers and allows them to be more readily pulled apart than unwaxed silk fibers and consequently waxed fibers have a lower tensile strength than unwaxed. When an unwaxed silk strand which has been imbedded in tissue comes in contact with bacteria, the strand may become a nidus of infection. The exposed end of an imbedded silk suture may act as a wick to carry infection to the tissue because of its capillarity. The practice of impregnatng wax into a braided silk strand was also adopted as a means of reducing capillarity.

It is a general object of this invention to provide silk sutures and ligatures which are impregnated with a polymeric substance and do not have the disadvantages inherent in wax impregnated silk strands.

It is a specific object of this invention to reduce the capillarity of silk sutures by impregnation with a polymeric substance.

A more specific object of this invention is to provide silk sutures and ligatures which are impregnated with a polymeric substance that are non-brooming, have high tensile strength, stiffness sufficient to facilitate the tying of knots, and good knot-holding properties.

It has now been discovered that the objects of this invention may be accomplished, in general, by the impreg- ICC evacuated to a pressure of not greater than 1 mm. of'

mercury. A solution of the impregnatng resing is thenf. introduced into the chamber in an amount sufficient to' completely immerse the spool. After a short period of` immersion under vacuum conditions, the vacuum is released and pressure in the chamber is allowed to come: to atmospheric. The thread is stripped of excess im pregnating solution and drawn through a pre-heat chamber and then through an aperture in a die maintained at: a temperature of about 250 C. to 300 C. It is pre-4 ferred that the aperture in the die have a diameter not exceeding by one mil the diameter of the silk thread orl strand. Passage of the heated impregnated silk strand? through the aperture of the heated die forces the melted resin into the taut strand and removes substantially all of any solvent still remaining. The strand is finally heated to set the resin and remove all traces of residual solvent bypassing it, as it cornes through the aperture of the heated die, through baking chambers in which the ternperature is preferably maintained at C. to 150 C.

Polymers of methacrylic acid esters having the following formula CHFC-COOR in which R is an alkyl radical having from three to six carbon atoms and copolymers of at least two different esters of methacrylic acid in which R in each ester is an alkyl radical having not more than 12 carbon atoms and in which the average number of carbon atoms in the R groups of the copolymers is within the range of three to six, have been found suitable for use as impregnants for surgical silk. The preferred polymeric substance is a copolymer of normal butyl methacrylate and normal hexyl methacrylate in which the ratio of the butyl to the heXyl ester is approximately three to one.

The amount of the polymeric substance impregnatng the silk thread or strand may be from two to twelve percent by weight but it is preferred that the amount be three to eight percent by weight.

An advantage of the surgical silk threads or strands. prepared according to this invention is that they may beA repeatedly flexed without cracking and have a slight: tackiness which facilitates knotting and provides good"` knot-holding properties to the strand. The method of' this invention for impregnatng the silk strands or threads.

provides for an even distribution of the polymeric sub-1 stance around the fibers of the thread and the polymeric substance is not stripped off or exuded when the thread is knotted. The thread treated with the polymeric sub-- stance does not broom when cut with a reasonably sharp! instrument because the silk fibers are firmly fixed together and the strand may be cut to a point to facilitate needle threading. Impregnation of surgical silk threads. or strands with the polymeric substance effects bonding of the silk fibers and at the same time imparts strength to the fibers and results in improved tensile strength of the silk threads or strands in general. Surgical silk strands or threads impregnated with the polymeric substance have increased resistance to wetting and water penetration and a minimum of capillary action when the strand is imbedded in bodytissue and in contact with tissue fluids.

Any conventional method of polymerization may be used in the preparation of the polymers or 'copolymers ofen ester ory esters Ofmethacrylic `acidbut. emulsion polymerization has been found particularly suitable. The following example is` given to illustrate the preparation of a polymeric `substance by emulsion polymerization.

Example I Four thousand grams of distilled water,'50 grams of sodium lauryl sulfate and 40 grams of benzoyl peroxide were thoroughly agitated in a 12-liter round bottom llask fitted with a stirrer, dropping funnel, thermometer, heating mantle, reux condenser, and `nitrogen inlet tube. TheA mixture was purgedv of oxygen during agitation by means of a continuous ow of nitrogen for one-half hour. A mixture of 1500 grams of monomeric n-.butyl methacrylate and 500 grams of ,monomeric n-hexyl methacrylate, from which any hydroquinone present as an inhibitor had been removed by washing with a 25% sodium carbonate-1% sodium hydroxide aqueous solution, was slowly introduced into the reaction ilask from the delivery cylinder with a simultaneous application t of heat to the reaction flask. By the time of completion of addition of the mixture of monomers the temperature of the reaction flask was 50 C. and agitation of the reaction mixture was continued for tive hours while the temperature was maintained at 50 C. After completion of the copolymerization, the entire reaction mixture was poured into twice its volume of methanol at room temperature and this resulted in the coagulation of the copolymer. The spongy coagulated copolymer was squeezed dry and extracted three times in boiling methanol. The copolymer was then thoroughly dried, pulverized and dissolved in yan amount of hot toluene such that the solution contained six percent of solids. The solution has a kinetic viscosity as measured by the method of Gardner-Holdt at 25 C. of 3.5 stokes.

A solution of the polymeric substance in an organic s01- vent is used for the impregnation of surgical silk strands. Any organic solvent in which the polymeric substance is sufliciently soluble to provide a solution having a kinetic viscosity in the range of 0.005 to strokes is suitable and such organic solvents, in addition to toluene, include Vxylene, acetone, ethyl acetate, methyl ethyl ketone and a liquid hydrocarbon such as high flash naphtha and mixtures thereof.

An impregnating solution containing the polymeric substance having a kinetic viscosity in the range of 0.005 to 10 Stokes may be used in the impregnation of surgical silk strands or threads according to the method of this invention, but it is preferred that the kinetic viscosity be within the range of from 2 to 6 stokes.

The following specific example illustrates the-preferred method of impregnating surgical silk strands or threads but is is not intended that the invention be construed as strictly limited to the method of the following example.

Example II A braided silk strand having a diameter of 14.5 to 15.0 mils was wound loosely on an open spindle type of spool and placed in a two-piece resin tlask tted with a long-stem separatory funnel and a vacuum take-ott in such a manner that the tip of the separatory funnel extended down into the open core of the spool. The impregnating chamber was evacuated toa pressure of 0.1 to 0.5 mm. of mercury and then the vacuum take-oit was closed and the six percent toluene solution of the polymeric substance, prepared according to Example I, was introduced into the chamber. The vacuum take-olf was released to the atmosphere a few seconds after the introduction of the impregnating solution into the chamber. The impregnated silk strand was drawn from theflaslc and passed through a wire loop to remove excess impregnating solution and to prevent the impregnating solution from beading along the strand, and then drawnthrough a vertical pre-heating column open at u, bothends `and heated to a temperature of 200 C. During the passage `Vofthe silk strandpthrough the pre-heating column, .the

polymeric substance became semi-fluid and a substantial amount of the toluene was removed. Immediately after the impregnated strand had passed through the preheating column, it was drawn through a funnel-shaped aperture in a stainless steel block about one inch in thickness, which was maintained at a temperature of 270 C. 'Ihe strand entered the aperture at the side having the largest diameter, 38 mils and emerged. from the aperture at the side having the smaller diameter,

15.8 mils.

The die block illustrated in the drawing has been found suitable for use in the impregnation of silk suture strands and in the drawing:

Figure l is atop view of the die block;

Figure 2 is a side view of the die block; and

Figure 3 is an enlarged drawing of a portion of onehalf of the die block showing the shape of the apertures and the passage of a silk suture strand through an aperture.

The die block, generally shown at 10, is composed of two halves, a front half 14 and a rear half 16; which are held together by a U-shaped holding member 12 attached to the rear half of ydie block 16 by bolts 18. The front half ofdie block 14 is firmly held against the rear half of die block 16 by screw 40 and the two halves of the die block are maintained in proper position by center ing and locking pegs 28 which are integral with the rear half of the die block 16. The pegs are set into holes 30 in the front half of .die block 14. By these means, the two halves of the die block are held tightly together such that edge 32 of the rear half of die block 16 and edge 34 of the front-half of die block 14 are pressed firmly together. The die block is heated by two heating units V22, which are inserted in heating unit wells 20 in the rear half of die block 16. The temperature of the dieblock is determined by means of thermo-couple 26, which is inserted in thermo-couple well 24 in the rear half of `the die block. Asshown in the drawing, and particularly `in Fig. 3, the die block contains three apertures `having a funnel shape for about one-half of their length 36. The measurements .020, .018, and .012 on Figures l and 3 represent the diameters of adjacent apertures at their narrowest part 38. The narrow part extends about one-half the length of the apertures and begins` where the funnel part ends. As illustrated in Figure 3, the silk suture strand S is pulled in the 'direction ofthe arrow so that it emerges from the aperture at its narrowest part, that is, the part represented by the diameters shown in the figures. The die block illustrated in the figures is constructed so that one-half of the aperture is in each half of `the die block; the one half of the aperture 36a is in the front half of die block 14, and the other half of the aperture 36b is in the rear half of the `.die block v16, the corresponding half of the aperture `38a is in the front half of the die block14, and the other half of the aperture 38b is in the rear half of the die block 16.

An aperture having the shape of a funnel for about one-half its length has been found particularly elective in impregnating a silk suture strand because =when a silk suture strand is passed through the funnel shaped portion and then through the narrowest portion, the impregnating polymericsubstance has been found to more thoroughly permeate and intimately contact the individual fibers of the strand.

Passage through `the heated die block had thc effect of more thoroughly impregnating the silk strand by forcing the resin uniformly throughout the body of thestrand andv giving a smooth surface and a uniform diameter to theimpregnated strand. It is preferred that the aperture in the die block be wider Iat the intake side than at the outgoing side and be funnel shaped over at least part ofits length and Vthat the diameter of the aperture at its narrowest point be about one mil greater than the average diameter of the silk strand before impregnation.

After theimpregnated strand was passed through the aperture in the die block, it was passed througha baking column maintained at 130 C. to 150 C. and wound on a spool. After passage through the baking column the impregnated strand was completely free from solvent. The speed with which the silk was passed through the preheating column, the aperture in the die block, and the baking column was six feet per minute. The speed with which a silk strand may be impregnated varies for diierent sizes of strands or threads and with the temperature of the baking column. Smaller sizes of silk strands may be processed at a faster rate than larger sizes because solvent evaporation from the former is faster.

The impregnated strand contained Veight percent by weight of the polymeric substance and had a diameter of 15.0 to 15.3 mils, a dry knot tensile strength of 7.22 pounds and a wet knot tensile strength of 5.52 pounds. The impregnated strand had a good hand and stiffness when wet or dry and didA not broom when cut with a sharp instrument.

The linear speed with which the silk strand is passed through the pre-heating column,the die block aperture and the baking column is related to the temperature to which the strand is subjected therein. At higher temperatures the speed is greater and if the temperatures are reduced the speed is reduced correspondingly. Examples III to VIII illustrate the preparation of six diierent polymeric substances. In these examples the method of polymerization was that of Example I except for the materials and amount used and specic reaction conditions which are 'given for each example.

Example III Grarns Methyl ester of methacrylic acid 33.3 Normal-hexyl ester of methacrylic acid 66.7 Water 200.0 Sodium lauryl sulfate 2.5 Benzoyl peroxide 1.0

The reaction was continued for four hours at 70 C. Six, nine, and twelve percent solutions of the polymeric substance in toluene had kinetic viscosities at 25 C. of 0.03, 0.18, and 0.41 stoke, respectively.

Example I V y l Grams Ethyl ester of methacrylic acid 40.0 Normal-hexyl ester of methacrylic acid 60.0 Water 200.0 Sodium lauryl sulfate 2.5 Benzoyl peroxide 1.0

The reaction was continued for two hours at 75 C. Six, nine, and twelve percent solutions of the polymeric substances in toluene had kinetic viscosities at 25 C. of 0.10, 0.18, and 0.27 Stokes, respectively.

The reaction was continued for two hours at 80 C. Six, nine, and twelve percent solutions of the polymeric substance in toluene had kinetic viscosities at 25 C. of 0.27, 1.12, and 3.1 stokes, respectively. y

Example VI Grams Methyl ester of methacrylic acid 66.7 Normal-lauryl ester of methacrylic acid 33.3 Water 200.0 Sodium lauryl sulfate Benzoyl peroxide 6 The reaction was continued for three hours at 80 C. Six, nine, and twelve percent solutions of the polymeric substance in toluene had kinetic viscosities at 25 C. of 0.03, 0.10, and 0.18 stokes, respectively.

Example VII t Grams Ethyl ester of methacrylic acid 60.0 Normal-octyl ester of methacrylic acid 40.0 Water g 200.0 Sodium lauryl sulfate 2.5 Benzoyl peroxide 1.0

The reaction was continued for three hours at C. Six, nine, and twelve percent solutions of the polymeric substances in toluene had kinetic viscosities at 25 C. of 0.18, 0.41, and 0.92 Stokes, respectively.

Example VIII Grams Normal-hexyl ester ot' methacrylic acid 100.0 Water 200.0 Sodium lauryl sulfate 2.5 Benzoyl peroxide 1.0

Tensile Strength Polymeric Substance legggg' Diameter From Example Substance Dry Knot Wet Knot (m1 (lbs.) (lbs.)

A braided silk strand of the same diameter impregnated with 22% beeswax had a dry knot tensile strength of 5.87 pounds and a wet knot tensile strength of 4.44 pounds. Y

All of the impregnated suture strands prepared according to this example had good hand, and stiffness both when wet and dry, and did not broom when cut with a sharp instrument.

Example X l Braided silk having a diameter of 14.0 to 14.5 mils was impregnated with a nine percent toluene solution of each of the polymeric substances prepared according to Examples III to VIII by the method of Example II. The following table gives the characteristics of the irnpregnated silk suture strands:

P tWt Tensile Strength Polymeric Substance Pflcen Diameter ymeric From Example Substance Dry Knot Wet Knot (mns) All of the impregnated suture strands prepared according to this example had good hand, and stiness both when wet and dry, and did not broom when cut with a sharpinstrument.

7 Example' Xl Braided silkzhaving a diameter of 14.0 to 14L5'mils was impregnated with a twelve percent toluene solution `of each of the polymerized substances prepared according to Examples III to VIII by the method of Example II. The following table gives the characteristics of the impregnated silk suture strands.

All of the impregnated suture strands prepared according to this example had good hand, and stiffness both wet and dry, and did not broom when cut with a sharp instrument, except the strand impregnated with the polymeric substance prepared according to Example V which was wiry and brittle, and had a poor hand.

Example XII A series of braided silk strands having diameters in mils of l2.0-l2.5, 9.5-10.0, 7.0-7.5, 5.5-6.0, and 2.0-2.5 were impregnated with a six percent toluene solution of the polymeric substanceprepared according to Example I. The following tables give the characteristics of the impregnated silk strands and of braided silk strands pregnated with approximately 22% beeswax of corre- All of the braided silkstrandsl impregnated `with the polymeric substance according to this example had good handand stiffness when wet or dry and did not broom when cut with a sharp instrument.

`Although in the practice of this invention, it is preferred that silk suture strands be impregnated according to the method illustrated in Example II, it has been found that satisfactory impregnated silk-suture strands may be generally made by contacting the strand with a solution of the polymeric substances listed above assuitable irnpregnating materials, followed by the removal of excess solution and airdrying at elevated temperatures and for a suflicient period of time `to remove allV of the volatile solvent. Such a means of impregnation may be repeated as many times as necessary in order that a sufticient amount of the polymeric substance may be impregnated into the strand.

After the silk suture strands have been impregnated they may be cut into required lengths, wound onto reels or into small coils and placed in glass tubes or other suitable receptacles whichmay then befsealed and heat sterilized at 155 C. for one hour. The autoclave method of sterilizing strands not hermetically sealedfin containers may also be employed.

Although the invention has been described with a certain degree ofrparticularity and with specifcv'reference to certain embodiments with respect to Lmethods of imthat it is not to be limited thereto, but 'itisto-be'com strued broadly and restricted solely by the scope of the claims.

What is claimed is:

1. A substantially noncapillary silk suture comprising a silk suture strand coated with a polymeric substance selected from the class consisting of polymers` and copolymers of methacrylc acid esters of the general formula omge-Coon in which, when the polymeric substance is a polymer, R is an alkyl radical having three to six carbon atoms and, when the polymeric substance is a copolymer, R is an alkyl radical having not more than twelve carbon atoms and an average number of carbon atoms within the range of three to six.

2. A substantially noncapillary silk suture comprising a silk suture strand coated with two to twelve percent by weight of a polymeric substance selected from the class consisting of polymers and copolymers'of methacrylic acid esters of the general formula in which, when the polymeric substance is a polymer, R is an alkyl radical having three to six carbon atoms and, when the polymeric substance is a copolymer, R is an alkyl radical having not more thantwelve carbon atoms and an average number of carbon atoms within the range of three to six.

3. A substantially noncapillary silkY suture comprising a silk suture strand coated with three to eight percent by weight of a polymeric substance selected from the class consisting of polymers and copolymers of methacrylic acid esters of the general formula CEPU-GOOR in which, when the polymeric substance is a polymer, R is an alkyl radical having three to six carbon atoms and, when the polymeric substance is a copolymer, R is an alkyl radical having not more than twelve carbon atoms and an average number of carbon `atoms within the range of three to six.

4. A substantially noncapillary silk suture comprising a silk suture strand coated with a copolymer of butyl rnethacrylate and hexyl rnethacrylate in whichthe ratio of the normal butyl to the normal hexyl ester is approximately three to one.

5. A substantially noncapillary silk suturer comprising a silk suture strand coated with two to twelve percent by weight of a copolymer of normal butyl rnethacrylate and normal hexyl rnethacrylate in which the ratio of the normal butyl to the normal hexyl ester, is approximately three to one.

6. A method of making a substantially noncapillary silk suture which includes the following steps: contacting a silk strand at reduced pressure with a solution in an organic solvent ofra polymeric substance, the solution having a kinetic viscosity within the range of 0.005 to 10 Stokes, the polymeric substance being selected from the class consisting of polymers and copolymers of methacrylic acid esters of the general formula oHr-C-G OOR (13H3 in which, when the polymeric substance is a polymer, R is an alkyl radicalV having three to six carbon atoms and, when the polymeric substance is a copolymer, R is an alkyl radical having not more than twelve carbon atoms and an average number of carbon atoms within the range of three to six; heating the strand to remove a` major amount of the solvent; and passing the strand througha heated die, whereby the polymeric substanceis made ud and becomes evenly distributedA throughout and 9 coated on the strand and substantially all the solvent is removed.

7. A method of making a substantially noncapillary silk suture which includes the following steps: contacting a silk suture strand at a pressure not greater than l mm. of mercury with a solution in an organic solvent of a polymeric substance selected from the class consisting or" polymers and copolymers of methacrylic acid esters of the general formula in which, when the polymeric substance is a polymer, R is an alkyl radical having three to six carbon atoms, and when the polymeric substance is a copolymer, R is an alkyl radical having not more than twelve carbon atoms and an average number of carbon atoms within the range of three to six; heating the strand to remove a major amount of the solvent; and passing the strand through a heated die, whereby the polymeric substance is made iluid and becomes evenly distributed throughout and coated on the strand and substantially all the solvent is removed.

8. A method of making a substantially noncapillary silk suture which includes the following steps; contacting a silk strand at reduced pressure with a toluene solution of a polymeric substance selected from the class consisting of polymers and copolymers of methacrylic acid esters of the general formula CEPU-GOOR in which, when the polymeric substance is a polymer, R is an alkyl radical having three to six carbon atoms and, when the polymeric substance is a copolymer, R is an alkyl radical having not more than twelve carbon atoms and an average number of carbon atoms Within the range of three to six; heating the strand to remove a major amount of the solvent, and passing the strand through a die maintained at a temperature of from 250 C. to 300 C., whereby the polymeric substance is made liuid and becomes evenly distributed throughout and coated on the strand and substantially all solvent is removed.

9. A method of making a substantially noncapillary silk suture which includes the following steps: contacting a silk strand at reduced pressure with a solution in an organic solvent of a polymeric substance selected from the class consisting of polymers and copolymers of methacrylic acid esters of the general formula CHF-'O O OOR in which, when the polymeric substance is a polymer, R is an alkyl radical having three to six carbon atoms and, when the polymeric substance is a copolymer, R is an alkyl radical having not more than twelve carbon atoms and an average number of carbon atoms within the range of three to six; heating the strand to remove a major amount of the solvent; passing the strand through a heated die, whereby the polymeric substance is made uid and becomes evenly distributed throughout and coated on the strand and substantially all the solvent is removed; and heating the strand to a temperature of from 130 C. to 150 C. whereby the solvent is completely removed from the strand.

10. A method of making a substantially noncapillary silk suture which includes the following steps: contacting a silk strand at reduced pressure with a solution in an organic solvent of a polymeric substance selected from the class consisting of polymers and copolymers of methacrylic acid esters of the general formula omo *C o o R (JH: in which, when the polymeric substance is a polymer, R

is an alkyl radical having three to six carbon atoms and, when the polymeric substance is a copolymer, R is an alkyl radical having not more than twelve carbon atoms and an average number of carbon atoms within the range of three to six; heating the strand to remove a major amount of the solvent; passing the strand through a die maintained at a temperature of about 250 C. to 300 C. whereby the polymeric substance is made uid and becomes evenly distributed throughout and coated on the strand and substantially all the solvent is removed; and heating the strand to a temperature of from C. to C; whereby all the remaining solvent is removed from the strand.

1l. A method of making a substantially noncapillary silk suture which includes the following steps: contacting a silk strand at a pressure not greater than l mm. of mercury with a solution in an organic solvent, of a copolymer of normal butyl methacrylate and normal hexyl methacrylate in which the ratio of normal butyl to normal hexyl ester is approximately three to one, heating the strand to remove a major amount of the solvent; and passing the strand through a die maintained at a temperature of about 250 C. to 300 C., whereby the polymeric substance is made fluid and becomes evenly distributed throughout and coated on the strand and substantially all the solvent is removed.

l2. A method of making a substantially noncapillary silk suture which includes the following steps: contacting a silk strand at a pressure not greater than 1 mm. of mercury with a toluene solution of a copolymer of normal butyl methacrylate and normal hexyl methacrylate in which the ratio of normal butyl to normal hexyl ester is approximately three to one and in which the kinetic viscosity of the toluene solution is within the range of 0.005 to 10 Stokes; heating the strand to remove a major amount of the solvent; passing the strand through a die maintained at a temperature of from 250 C. to 300 C., whereby the polymeric substance is made uid and becomes evenly distributed throughout and coated on the strand and substantially all the solvent is removed; and heating the strand to a temperature Within the range of 130 C. to 150 C. whereby all remaining solvent is removed from the strand.

13.\A method of making a substantially noncapillary silk suture which includes the following steps: contacting a silk strand at reduced pressure with a solution in an organic solvent of a polymeric substance selected from the class consisting of polymers and copolymers of methacrylic acid esters of the general formula CHFC-COOR in which, when the polymeric substance is a polymer, R is an alkyl radical having three to six carbon atoms and, when the polymeric substance is a copolymer, R.is an alkyl radical having not more than twelve carbon atoms and an average number of carbon atoms within the range of three to six; heating the strand to remove a major amount or" the solvent; and passing the strand through a heatedy die, whereby the polymeric substance is made iluid and becomes evenly distributed throughout and coated on the strand and substantially all the solvent is removed.

References Cited in the le of this patent UNITED STATES PATENTS 2,046,886 Strain July 7, 1936 2,193,188 Bradley Mar. l2, 1940 2,344,494 Camp Mar. 21, 1944 2,462,895 Quinn Mar. 1, 1949 

1. A SUBSTANTIALLY NONCAPILLARY SILK SUTURE COMPRISING A SILK SUTURE STRAND COATED WITH A POLYMERIC SUBSTANCE SELECTED FORM THE CLASS CONSISTING OF POLYMERS AND COPOLYMERS OF METHACRYLIC ACID ESTERS OF THE GENERAL FORMULA 